Phase relationship in LaAl2−xSix (0 ≤ x ≤ 1.03) and their electrical resistivity

The ternary silicides LaAl2−xSix with x ranging from 0 to 1.03 were synthesized by Ar-arc melting. The crystal structure of LaAl2−xSix depends on the Si content x: the Cu2Mg-type structure for 0 ≤ x ≤ 0.005, the AlB2-type for 0.14 ≤ x ≤ 0.62, and the α-ThSi2-type for 0.72 ≤ x ≤ 1.03. The range of x at which the AlB2 phase appears was wider than that reported previously. In the AlB2 phase, the lattice constants a and c change anisotropically with x: a decreases with x, while c increases with x. On the other hand, in the α-ThSi2 phase, both a and c decrease with x. The electrical resistivity measurements at temperatures ranging from 2 to 300 K revealed that the AlB2 phase and the α-ThSi2 phase LaAl2−xSix are metals that show no superconductivity down to 2 K.